Merge Queue Test Repository

This repository is set up to test GitHub's merge queue functionality, including SHA behavior, queue ordering, and handling of failed checks.

Setup

1. Enable GitHub Actions in your repository settings if not already enabled.

2. Set up branch protection and merge queue:

   # Make sure you have GitHub CLI installed and authenticated
   ./setup-branch-protection.sh

3. Create sample files for testing:

   ./create-sample-files.sh

Testing Scenarios

Understanding SHA Behavior

The workflows include detailed SHA logging to help understand:

• How SHAs change when PRs enter the merge queue
• The difference between PR head SHA and merge queue SHA
• How merge commits are created in the queue

Test Case 1: Single PR in Queue

1. Create a new branch and make changes:

   git checkout -b feature/test-1
   echo "Test 1" > test1.txt
   git add test1.txt
   git commit -m "Add test1.txt"
   git push origin feature/test-1

2. Create a PR and observe:

   • Initial PR SHA in the checks
   • After approval, add to merge queue
   • New merge queue SHA (different from PR SHA)
   • Check results with the new SHA

Test Case 2: Multiple PRs in Queue

1. Create multiple PRs quickly:

   ./create-multiple-prs.sh 3

2. Approve all PRs and add them to the merge queue simultaneously

3. Observe:

   • How PRs are grouped in the queue
   • SHA changes for each PR when entering the queue
   • Order of processing
   • How failure of one PR affects others

Test Case 3: Handling Failed Checks

The repository includes intentionally flaky tests:

• flaky-test: 30% failure rate
• unstable-integration: 50% failure rate
• timing-sensitive: Fails during minutes ending in 3, 6, or 9

To test failure scenarios:

1. Create a PR and add to merge queue
2. If all checks pass, close and retry (statistically, you'll hit failures)
3. Observe:
   • How the merge queue handles failures
   • Whether the PR is removed from queue
   • If other PRs in queue are affected

Test Case 4: Queue Ordering and Dependencies

1. Create PRs with different priorities:

   # Create a large PR
   git checkout -b feature/large-change
   for i in {1..10}; do echo "Line $i" >> large-file.txt; done
   git add large-file.txt
   git commit -m "Large change"
   git push origin feature/large-change
   
   # Create a small urgent fix
   git checkout main
   git pull
   git checkout -b fix/urgent
   echo "urgent fix" > urgent.txt
   git add urgent.txt
   git commit -m "Urgent fix"
   git push origin fix/urgent

2. Add both to merge queue and observe processing order

Debugging Tips

Viewing SHA Information

Each workflow run logs detailed SHA information:

• Check the "Show SHA information" step in any workflow run
• Compare PR SHA vs merge queue SHA
• Track how SHAs change through the process

Understanding Merge Queue Events

The workflows differentiate between:

• pull_request events (normal PR checks)
• merge_group events (merge queue checks)

Look for "Event Name" in the logs to understand the context.

Monitoring Queue Status

Use GitHub's merge queue UI:

1. Go to the Pull Requests tab
2. Click on "Merge Queue" to see current queue status
3. Observe position, estimated time, and check status

Common Issues and Solutions

Issue: Checks failing in merge queue but passing in PR

• Cause: Different SHA or merge conflicts
• Solution: Check SHA differences in logs, ensure base branch is up-to-date

Issue: PRs stuck in queue

• Cause: Consistently failing flaky tests
• Solution: Re-run failed checks or temporarily disable flaky tests

Issue: Queue processing seems slow

• Cause: Conservative queue settings or many failing checks
• Solution: Adjust max_entries_to_merge and min_entries_to_merge in setup script

Advanced Testing

Simulating Production Conditions

1. High traffic: Use create-multiple-prs.sh with higher numbers
2. Complex conflicts: Create PRs that modify same files
3. Long-running tests: Modify workflows to add delays

Analyzing Queue Performance

Track metrics:

• Time from PR approval to merge
• Queue failure rate
• Impact of grouping strategies

Cleanup

To remove test branches after testing:

# List all test branches
git branch -r | grep 'origin/feature/test-\|origin/fix/' 

# Delete remote branches
git push origin --delete feature/test-1 feature/test-2 # etc